Field of the Invention
This invention relates to an apparatus and method for imaging human tissue which use geometrically registered X-ray and ultrasound imaging techniques. In particular, the invention relates to improvements to existing dual-modality mammography equipment which uses a combination of such techniques, as well as to apparatus for augmenting and improving conventional mammography equipment.
Description of the Related Art
Dual-modality imaging systems that use a combination of full-field digital mammography and automated breast ultrasound imaging in a single device are known. These devices combine the benefits of both imaging techniques to obtain more effective and accurate diagnosis of carcinoma or other abnormalities in particularly breast tissue.
The applicant's international patent application number WO2011/153555 entitled “DUAL-MODALITY SCANNING SYSTEM FOR DETECTING BREAST CANCER” discloses such a dual-modality scanning apparatus that incorporates both X-ray and ultrasound technologies. The apparatus at least partially alleviates a number of problems experienced with other previously known dual-modality apparatus and meets five specific functional attributes including: (1) that the breast is in the same orientation and degree of compression when X-ray and ultrasound images are obtained; (2) that both sets of images are acquired simultaneously so as to minimize the time the patient's breast is held stationary and compressed between the compression plates; (3) that automated breast ultrasound images of the whole breast are acquired in a single scan; (4) that both image modalities are acquired in three dimensions (3D); and (5) that radiation dose exposure to the patient is minimized.
To achieve these functional attributes the apparatus comprises an X-ray source arranged to generate an output beam having a reference axis; a pre-collimator arranged to modify the output beam to generate a fan beam; a platform defining a first surface for supporting a breast of a patient; a first drive arranged to move the pre-collimator transverse to the reference axis, thereby to impart motion to the fan beam; a linear scanning element comprising an X-ray sensor and an ultrasound transducer supported adjacent to and beneath the first surface and extending parallel to the fan beam and reference axis; a second drive arranged to move the linear scanning element transverse to the reference axis, in synchronisation with the first drive, while both x-ray and ultrasound scanning are being conducted, thereby to generate a two-dimensional X-ray image and a three-dimensional ultrasound image of the breast; a third drive arranged to rotate the X-ray source relative to the platform, thereby to generate a plurality of sets of two-dimensional X-ray images of the breast for tomosynthesis purposes; and a processor for implementing tomosynthesis reconstruction algorithms to generate three-dimensional X-ray and ultrasound images, and to co-register the three-dimensional X-ray and ultrasound images.
In use, the tissue to be scanned, typically a breast, is compressed between the first surface and a compression plate which is mechanically lowered onto the breast so as to effect the compression in order to pull as much of the breast tissue from the chest wall as possible and spread the breast tissue out across the platform to a uniform thickness. This compression separates out overlying breast structures and improves image clarity obtained by the X-ray and ultrasound scanners. In addition, the more the breast tissue can be compressed, the lower the X-ray dosage will be that is required to conduct effective X-ray scanning. However, due to the discomfort generally associated during significant compression of the breast tissue, excessive compression is not desirable.
WO2011/153555 is incorporated herein, in its entirety, by reference.
In the apparatus described in WO2011/153555 as well as other known dual-modality scanning devices, the automated ultrasound transducer is generally mounted below or above one of the compression surfaces, as the case may be, which in turn are substantially in direct contact with the breast being scanned while simultaneously immobilising the breast and maintaining uniform compression thickness of the breast tissue. To avoid contact and possible damage caused by contact between the X-ray detector or ultrasound transducer and compression surface below or above which it is mounted during scanning, the X-ray detector and ultrasound transducer are generally mounted slightly removed from the compression surface. A disadvantage of this configuration is that it necessitates the impending X-ray radiation and ultrasonic waves to move through regions of air before reaching the X-ray detector, compression platform or ultrasound transducer, as the case may be. This results in impedance mismatches and acoustic reflection of the ultrasonic waves at the compression platform interface, which in turn negatively affects the ultrasound images obtained, as well as potential X-ray signal attenuation and geometric blurring due to the finite X-ray focal point. As compression of the breast can also result in temporary deformation of the compression surface, the distance at which the X-ray detector and ultrasound transducer have to be mounted from the compression surface has to be sufficient to accommodate the deformation while avoiding contact with the scanning surface during scanning.
In addition to the impedance mismatch at the compression platform interface, the problem for the ultrasound imaging is exacerbated at the outermost extremities (most distal parts) of the breast between the compression surfaces. At these distal portions, the natural curvature of the breast creates spaces which act as air barriers between the breast tissue and the compression surfaces to the generally perpendicular ultrasound beams emitted by the linear transducer on the opposite side of one of the compression surfaces. This results in a peripheral volume of the breast not being accessible, or being poorly accessible, to the ultrasound beams, yielding inferior imaging of the breast in these regions. To alleviate this problem the ultrasound beams need to be steered appropriately into the peripheral volume of the breast.
Despite previous efforts in developing imaging systems, including those described in U.S. Pat. Nos. 8,325,877; 7,313,259; 6,846,289; 6,574,499; 6,876,879; 6,682,484; 3,480,002; 4,433,690; 6,971,991; 7,831,015; 8,376,946; 7,496,398; 5,872,828; 4,567,895; 7,739,912; 5,474,072; 5,479,927; 7,916,918; 8,326,006; 8,323,201; 8,206,307; 5,640,956; 5,303,281; 7,940,890; 4,432,371; 7,264,592; 5,474,072; 5,479,927; 5,664,573; 5,938,613; 5,983,123; 3,964,296; 4,130,112; and U.S. Application Publication Nos. 20080234578; 20080242979; 20030149364; 20050288581; 20120245463; 20070055159; 20110224551; 20060241423; 20080255452; 20100256490; 20060074287; 20070263768; International Application Publication Nos. WO2008144274, WO00/09014, WO2004030523, WO2004107960, WO2006015296, WO2011153555; European Patent No. 0730431; UK Patent Application No. GB2025617; German Patent Application No. DE19901730A1; German Patent No. DE 29914663 U1, as well as those described in various non-patent literature (See Booi et al., Evaluating Thin Compression Paddles For Mammographically Compatible Ultrasound, Ultrasound in Med. & Biol., Vol. 33, No. 3, pp. 472-482, 2007; Goodsitt et al., Automated Registration of Volumes of Interest for a Combined X-Ray Tomosynthesis and Ultrasound Breast Imaging System, Lecture Notes in Computer Science Volume 5116, 2008, pp 463-468; Irving et al., Radiation Dose From A Linear Slit Scanning X-Ray Machine With Full-Body Imaging Capabilities Radiation Protection Dosimetry (2008), Vol. 130, No. 4, pp. 482-489; Novak, Indications for and Comparative Diagnostic Value of Combined Ultrasound and X-Ray Mammography, Europ. J. Radiol. 3 (1983) 299-302; Sinha et al., Multi-modality 3D breast imaging with X-Ray tomosynthesis and automated ultrasound, Proceedings of the 29th Annual International Conference of the IEEE EMBS Cite Internationale, Lyon, France, Aug. 23-26, 2007; Suri et al., Fischer's Fused Full Field Digital Mammography and Ultrasound System (FFDMUS)), Medical and Care Compunetics 2, p 177-200, 2005; and Tesic et al., Full field digital mammography scanner, European Journal of Radiology 31 (1997) 2-17), each of which is hereby incorporated by reference herein in its entirety, there is still a need for improvements to existing dual-modality scanning apparatus which will at least partially alleviate the problems mentioned above.